public class ResolvingDecoder extends ValidatingDecoder
Decoder
that performs type-resolution between the reader's and
writer's schemas.
When resolving schemas, this class will return the values of fields in
_writer's_ order, not the reader's order. (However, it returns _only_ the
reader's fields, not any extra fields the writer may have written.) To help
clients handle fields that appear to be coming out of order, this class
defines the method readFieldOrder()
.
See the parser documentation for information on how this works.
in
parser
Modifier and Type | Method and Description |
---|---|
Symbol |
doAction(Symbol input,
Symbol top)
Handle the action symbol top when the input is
sought to be taken off the stack.
|
void |
drain()
Consume any more data that has been written by the writer but not
needed by the reader so that the the underlying decoder is in proper
shape for the next record.
|
ByteBuffer |
readBytes(ByteBuffer old)
Reads a byte-string written by
Encoder.writeBytes(java.nio.ByteBuffer) . |
double |
readDouble()
Reads a double written by
Encoder.writeDouble(double) . |
int |
readEnum()
Reads an enumeration.
|
Schema.Field[] |
readFieldOrder()
Returns the actual order in which the reader's fields will be
returned to the reader.
|
float |
readFloat()
Reads a float written by
Encoder.writeFloat(float) . |
int |
readIndex()
Reads the tag of a union written by
Encoder.writeIndex(int) . |
long |
readLong()
Reads a long written by
Encoder.writeLong(long) . |
String |
readString()
Reads a char-string written by
Encoder.writeString(org.apache.avro.util.Utf8) . |
Utf8 |
readString(Utf8 old)
Reads a char-string written by
Encoder.writeString(org.apache.avro.util.Utf8) . |
static Object |
resolve(Schema writer,
Schema reader)
Produces an opaque resolver that can be used to construct a new
ResolvingDecoder(Object, Decoder) . |
void |
skipAction()
Skips the action at the top of the stack.
|
void |
skipBytes()
Discards a byte-string written by
Encoder.writeBytes(java.nio.ByteBuffer) . |
void |
skipString()
Discards a char-string written by
Encoder.writeString(org.apache.avro.util.Utf8) . |
arrayNext, configure, mapNext, readArrayStart, readBoolean, readFixed, readInt, readMapStart, readNull, skipArray, skipFixed, skipFixed, skipMap
skipTopSymbol
public static Object resolve(Schema writer, Schema reader) throws IOException
ResolvingDecoder(Object, Decoder)
. The
returned Object is immutable and hence can be simultaneously used
in many ResolvingDecoders. This method is reasonably expensive, the
users are encouraged to cache the result.writer
- The writer's schema. Cannot be null.reader
- The reader's schema. Cannot be null.IOException
public final Schema.Field[] readFieldOrder() throws IOException
ResolvingDecoder
returns values in the order written by the writer, rather than
the order expected by the reader. This method allows readers
to figure out what fields to expect. Let's say the reader is
expecting a three-field record, the first field is a long, the
second a string, and the third an array. In this case, a
typical usage might be as follows:
Schema.Fields[] fieldOrder = in.readFieldOrder(); for (int i = 0; i < 3; i++) { switch (fieldOrder[i].pos()) { case 1: foo(in.readLong()); break; case 2: someVariable = in.readString(); break; case 3: bar(in); // The code of "bar" will read an array-of-int break; }Note that
ResolvingDecoder
will return only the
fields expected by the reader, not other fields that may have
been written by the writer. Thus, the iteration-count of "3" in
the above loop will always be correct.
Throws a runtime exception if we're not just about to read the
field of a record. Also, this method will consume the field
information, and thus may only be called once before
reading the field value. (However, if the client knows the
order of incoming fields, then the client does not
need to call this method but rather can just start reading the
field values.)AvroTypeException
- If we're not starting a new recordIOException
public final void drain() throws IOException
IOException
public long readLong() throws IOException
Decoder
Encoder.writeLong(long)
.readLong
in class ValidatingDecoder
IOException
public float readFloat() throws IOException
Decoder
Encoder.writeFloat(float)
.readFloat
in class ValidatingDecoder
IOException
public double readDouble() throws IOException
Decoder
Encoder.writeDouble(double)
.readDouble
in class ValidatingDecoder
IOException
public Utf8 readString(Utf8 old) throws IOException
Decoder
Encoder.writeString(org.apache.avro.util.Utf8)
.readString
in class ValidatingDecoder
IOException
public String readString() throws IOException
Decoder
Encoder.writeString(org.apache.avro.util.Utf8)
.readString
in class ValidatingDecoder
IOException
public void skipString() throws IOException
Decoder
Encoder.writeString(org.apache.avro.util.Utf8)
.skipString
in class ValidatingDecoder
IOException
public ByteBuffer readBytes(ByteBuffer old) throws IOException
Decoder
Encoder.writeBytes(java.nio.ByteBuffer)
.
if old is not null and has sufficient capacity to take in
the bytes being read, the bytes are returned in old.readBytes
in class ValidatingDecoder
IOException
public void skipBytes() throws IOException
Decoder
Encoder.writeBytes(java.nio.ByteBuffer)
.skipBytes
in class ValidatingDecoder
IOException
public int readEnum() throws IOException
Decoder
readEnum
in class ValidatingDecoder
IOException
public int readIndex() throws IOException
Decoder
Encoder.writeIndex(int)
.readIndex
in class ValidatingDecoder
IOException
public Symbol doAction(Symbol input, Symbol top) throws IOException
Parser.ActionHandler
doAction
in interface Parser.ActionHandler
doAction
in class ValidatingDecoder
input
- The input symbol from the caller of advancetop
- The symbol at the top the stack.IOException
public void skipAction() throws IOException
SkipParser.SkipHandler
skipAction
in interface SkipParser.SkipHandler
skipAction
in class ParsingDecoder
IOException
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